2-15
RT765E-2 SERVICE MANUAL HYDRAULIC SYSTEM
Published 9-04-2014, Control # 422-08
OIL COOLER
Description
An air cooled hydraulic/transmission cooler (Figure 2-3) is
located next to the hydraulic tank. The front section is the
transmission oil cooler and the rear section is the hydraulic
oil cooler.
The hydraulic driven fan pulls cool air through the cooling
fins on the cooler. Normally most hydraulic oil from
components is routed through the oil cooler by way of a
return line, and on to the filter in the reservoir. When several
hydraulic functions are being used at one time (i.e., hoisting,
lifting, and telescoping), more oil has to flow through this
return line, causing a pressure buildup. When this pressure
reaches 15 psi (100 kPa), the normally closed check valve in
the return line (in parallel with the return line through the
hydraulic oil cooler) will open, letting some hydraulic oil
bypass the hydraulic oil cooler and flow directly into the
reservoir filter.
When fewer functions are being used, the pressure in the
system will decrease below 15 psi 100 kPa and the check
valve will close again.
Oil Temperature Switches
A hydraulic oil high temperature indicator switch (4),
Figure 2-1 and two oil cooler fan motor temperature switches
(6 and 7) are installed in the return tube. The two oil cooler
fan motor temperature switches are normally closed at low
oil temperatures. When the hydraulic oil temperature
reaches 120 °F (48.9 °C), one of the oil cooler fan motor
temperature switch will open, causing the CANbus system to
turn on the oil cooler fan motor to its low rpm setting. When
the hydraulic oil temperature reaches 180 °F (82.2 °C), the
other oil cooler fan motor temperature switch will open,
causing the CANbus system to increase the rpm of the oil
cooler fan motor to high. The hydraulic oil high temperature
indicator switch is normally closed and will open when the
hydraulic oil temperature reaches 190 °F (87.8 °C), causing
the CANbus system to turn on the hydraulic oil high
temperature indicator in the gauge cluster to alert the
operator to the condition.
Temperature switch (5, Figure 2-3), located in the inlet tube
of the transmission oil cooler, is part of a circuit that will alert
the operator to a high transmission oil temperature condition.
The switch is normally closed and will open and cause the
circuit to lose ground when the transmission oil temperature
exceeds 200°F (93°C). When the circuit loses ground, the
CAN bus system will turn on power to illuminate the
Transmission Warning Indicator in the gauge display in the
operator’s cab. See Section 3 - Operating Controls and
Procedures, in the Operator’s Manual for details of the
Transmission Warning Indicator.
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